What is Short Increment Sensitivity Index (SISI)?

SISI is a test of the ability of an individual to recognise 1dB increases in intensity during a series of pure tone bursts. This was designed to assist in the determination of where the hearing impairment arose from.

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Why use SISI?

In the management of hearing impairments, it is important to understand where the issue arises from, whether it is cochlear or retrocochlear. In a cochlear disorder, the patient will be able to differentiate the 1dB steps whereas an individual who has a retrocochlear disorder will not.

How to perform SISI?

A continuous tone is presented at the test frequency and at a sensation level of 20dB above the threshold for that frequency. Every 5 seconds a short 1dB increment is super-imposed over the continuous tone for approximately 200msec. The client is asked to signal the examiner that they have detected an incremental increase. The possibility of false positives or false negatives is reduced by the interspersion of 5dB increments after every five test presentations. After the presentation of 20 test increments, a percentage score can be derived by multiplying the number of increments by five.

Results can be interpreted as:

70%-100% correct = high (cochlear loss)
20-70% correct = inconclusive
<20% = low (retrocochlear loss)